Water-base flaw detection method

ABSTRACT

A method of detecting flaws in metallic and other insoluble surfaces which method utilizes a normally solid composition with coloring in a hot aqeuous solution. The hot aqueous solution is applied to the surface and upon drying solidifies. The surface coating is removed but the composition which has dried in surface openings and flaws is retained. The retained colored composition marks the location of surface discontinuities and, as it is a solidified composition, it is more resistant to over-removal, than the ordinary colored liquid composition now used, when the surface coating is being removed.

Dec. 4, 1973 WATER-BASE FLAW DETECTION METHOD Inventors: Dale D. Winans, 27115 Sunny Ridge Rd., Rolling Hills, Calif. 90274; Amos G. Sherwin, 8330 Gainford St., Downey, Calif. 90240 [22] Filed: Oct. 30, 1972 [21] Appl. No.: 302,284

[52] [1.8. CI. 250/302 [51] Int. Cl. G01n 21/38 [58] Field of Search 250/7l T, 302

[56] References Cited UNITED STATES PATENTS 3,028,338 4/1962 Parker, Jr 250/71 T X Primary Examiner.lames W. Lawrence Assistant Examiner-Davis L. Willis [57] ABSTRACT A method of detecting flaws in metallic and other insoluble surfaces which method utilizes a normally solid composition with coloring in a hot aqeuous solution. The hot aqueous solution is applied to the surface and upon drying solidifies. The surface coating is removed but the composition which has dried in surface openings and flaws is retained. The retained colored composition marks the location of surface discontinuities and, as it is a solidified composition, it is more resistant to over-removal, than the ordinary colored liquid composition now used, when the surface coating is being removed.

6 Claims, N0 Drawings 1 WATER-BASE FLAW DETECTION METHOD This patent is concerned with a process for detection of flaws in metal and other surfaces. lts principle is a hot water solution made up of ingredients which dry to an immobile or nonliquid state which ingredients carry a coloring material; The solution is applied to a surface where it enters openings and discontinuities. It is allowed to dry to an immobile or nonliquid condition. The surface'is then washed with water until the ingredients on the surface are dissolved, eroded and otherwise removed from the surface, leaving entrapped in the discontinuities the colored immobile ingredients. The color, whether visible under natural light or fluorescent under ultraviolet light, either with or without the aid of a developing agent, marks the location of the break or opening in the surface.

It could be stated that this invention is related to or in the category of liquid penetrant inspection, but is novel because the crack retained residue is not a liquid and is novel because the penetrating colored liquid is applied hot. Those familiar with the liquid penetrant inspection art will recognize the advantages'of this process.

The penetrant process for locating cracks and similar discontinuities in metal and other nonsoluble surfaces normally consists of an oily penetrating liquid charged with either fluorescent dyestuff or visible dyestuff which liquid can be either a water-soluble composition or a nonwater-soluble composition. The penetrating liquid is applied to the surface by dipping the test part into the liquid, spraying or painting the liquid on the surface or by any convenient means and then allowed to dwell for sufficient time for the penetrating liquid to enter the surface openings. The next step is to remove the penetrating liquid from the surface without removing that which has migrated into the crack or cracks. If the penetrating liquid is water-soluble, a water-spray wash is commonly employed to remove the liquid from the surface and special care must be taken to not overwash. The force of the spray must not be too great and the length of the wash must not be over-extended. The objective is to remove the liquid on the surface without removing the liquid in" the flaw. If the penetrating liquid is of the nonwaterwashable type, then it isremoved by applying a second liquid which is waters oluble. .This second liquid blends with the penetrating liquid, so the penetrating liquid becomes water-soluble and then the two liquids are washed from the surface. In this instance, special care must be taken that the second liquid remains on the surface only long enough to blend with the first liquid that is on the surface and not long enough to blend with and displace the penetrating liquid which has found its way into the crack. The nonwater-washable penetrating liquid, in lieu of the second water-soluble liquid overlayer procedure can be wiped from the surface, but this is tedious. Next, the surface is dried and either with or without a developing agent which is normally some form of powder, the surface is examined for colored marks either under ultra-violet light for fluorescent or under normal light for visible, which would indicate surface discontinuities.

The success of the process depends in very great part on the discontinuity being open to the liquid, for if the discontinuity is already filled with some form of soil such as oil or grease the liquid will not be able to enter the already full discontinuity. Therefore, cleaning prior to applicationof the liquid is normally a part of the process. Cleaning is often a hot alkaline detergent water solution into which the parts to be inspected are immersed for a given amount of time, removed and rinsed in clear hot water and then dried in an oven and cooled before the liquid used to locate flaws is applied. Another popular method of cleaning before application of the penetrant liquid is vapor degreasing. Here the parts to be inspectedare placed in a chamber containing a chlorinated or similar type solvent which is heated until vaporized. The parts are left in the vapor degreaser until they become quite hot. As they are removed the vapor is cooled and drains back into the chamber.

It is customary to allow the parts to cool following hot cleaning processes whether hot aqueous solution cleaning or vapor degreasing before immersion in the oily penetrating liquid to avoid heating the liquid and vaporizing the lighter fractions. Our invention eliminates the need to pre-cool the parts and results in saving considerable processing time.

Further, when a hot aqueous cleaner, followed by a hot aqueous rinse is the cleaning method, there is no need to dry the part b'efore immersion in the hot water solution of this invention. This saves a processing step.

A principle cause of failure of the liquid penetrant process is foreign matter in the surface discontinuity which foreign matter or contaminant blocks the entry of the penetrating liquid. A contaminant very effective in preventing entry of .a conventional penetrant liquid is water, either as an atmospheric condensation or as a residue from previous processing. Other solvents remaining in discontinuities from previous processing, depending on such factors as relative surface tension, may block or repel the entry of the penetrating liquid. Also effective in restricting entry of the penetrating liquid are waxy substaces such as paraffin and heavier greases which remain from previous processing or from the environment to which the test body was exposed.

Our invention will eliminate or substantially reduce the above described causes of failure of the liquid penetrant process. Condensed water in the discontinuity will be displaced almost immediately upon immersion of the test body in the hot water solution and will not restrict entry. 3

A's will be observed from fortn'ulations presented later, these hot water solutions may have detergent properties. So, the liquid used in our invention may have both heat and detergency for cleaning function. It may combine cleaning properties with discontinuity marking properties. Therefore, other solvents such as light petroleum solvents are removable in the hot water solution. The greases and waxy substances relatively immobile and difficult to remove from discontinuities at normal temperatures, will becomemore fluid and removable when immersed in the hot solution as the heat is transferred to and has a melting effect on the contaminant.

Another cause of failure of the liquid penetrant process is failure of'the penetrant to enter a flaw within the given dwell time. The rate of migration is largely dependent upon the viscosity of the penetrating liquid, other factors being equal, with the thicker or viscous liquids having a much slower rate of penetration than thin or nonviscous liquids. Temperature influences viscosity with the viscosity lower at higher temperatures. The hot aqueous solution penetrant has a far faster penetrating rate than a cold aqueous solution due to its lower viscosity.

Perhaps, the major cause of failure of the liquid penetrant process to mark flaw of discontinuity locations on the test body s surface is the inability of the penetrating liquid to remain entrapped. The penetrating liquid is migratory and once the surface is free of penetrating liquid, its affinity for the surface will draw it from the discontinuity, returning some or all of the entrapped penetrating liquid to the surface, lowering the intensity and sharpness of its discontinuity mark. The bleeding of the penetrating liquid, at its worse, can spread the liquid on the surface is such a thin film as to make the flaw mark indiscernible. Our invention reduces or eliminates bleeding as the discontinuity entrapments are not in liquid form but are solidified, relatively incapable of migration.

Another reason for failure of the liquid penetrant process to remain entrapped in the discontinuity is over-removal. In describing the conventional penetrant process we mentioned the water-soluble composition where the timing of the wash and pressure of the wash were extremely important to avoid removal of the liquid penetrant which has found its way into surface discontinuities. If the wash is extended, the entrapped watersoluble liquid will be dissolved in the water and the process defeated. At best, it must be anticipated that some wash water will mix with the entrapped penetrating liquid and indications will be weaker. Also mentioned was the nonwater-soluble penetrating liquid composition which requires a second water-soluble liquid to be applied over it, so the two liquids can blend and be washed from the surface. Here the trick is to time the blending so surface removal is accomplished with a water-wasli but without allowing the second liquid to blend with or displace discontinuity entrapped penetrating liquid. Even if this is accomplished, the entrapped liquid is still subject to water erosion during the phase of the process where the blended liquids are washed from the surface.

Our invention minimizes this cause of failure, re-

moval of the discontinuity entrapped composition during the excess or surface composition removal phase of the process, as the entrapped composition is more resistant to dislodgment, being a-nearly immobile state or solid state, and is also more resistant to beingdissolved in the wash water. The entrapped composition while readily soluble in hot water is slow to dissolve in cold water as normally used for rinsing.

Another cause for failure in the conventional liquid penetrant process is over-heating during the drying step prior to developer application. The conventional penetrating liquid if the oven temperature exceeds recommended temperatures, usually about 180 F, by only 40 or 50, or if the oven dwell time is over-extended, will partially volatize, leaving an inadequate responding residue, in the discontinuity. Our invention will not have this propensity. The discontinuity entrapment will not materially volatize at temperatures normally considered excessive or at oven dwell times which prove excessive to existent penetrating liquids, although the entrapment may creep from a melting effect when exposed to excessive heating.

Penetrating liquid are usually oil-base and, as such, represent a water pollution source of some consequence. It has been recognized that wate'rbase penetrants minimize pollution potential for sometime but until our invention water-base penetrants were not effective due to this propensity to overwash or, stated another way, the solubulizing of the discontinuity entrapment was too rapid to make a water-base penetrant a completely reliable tool. No petroleum solvents will be introduced into the waste water by the compositions used in our invention.

Our process is the application to the surface of the test body by any convenient means including spraying, brushing or immersion, with the latter method primarily recommended if precleaning has been inadequate in order to utilize the cleaning capabilities of the solution, of a hot aqueous solution which may include but is not restricted to a nonionic surfactant of relatively high ethylene oxide mole ratio and one or more dyestuffs either visible under white light or ultra violet light or both. A formula we have found to perform very well is the following:

1. One part Nonylphenol Ethoxylate with 20 moles of ethylene oxide to which has been added 1 percent by weight dyestuff Solvent Yellow 44 and 3 percent by weight dyestuff Fluorescent Brightner 61.

2. One part Polyethylene Glycol with molecular weight of 20000 to which has been added 2% by weight Fluorescent Brightner 61.

A source for ingredient (1) is Union Carbide Corporation, New York, New York, whose tradename for this product is Tergitol NP40 and a source for ingredient (2) is Dow Chemical, Midland, Michigan whose tradename for this product is Polyglycol E 20000.

The melting points of both of these ingredients is over 68 F. A practical way to introduce the dyestuffs is to first heat the ingredients until they are fluid then add the dyestuffs, stirring, and maintaining heat until they are visibly in solution. Depending on manufacturing advantages blending of the ingredients 1 and 2 can take place either before or during or after dyestuff introduction. Upon cooling the ingredients will become immobile. For later mixing in a hot aqueous solution, it may be to advantage to add some water at this time to keep the ingredients fluid. We have found that the addition of equal parts water is practical. The water may carry corrosion inhibiting agents such as sodium nitrite and sodium chromate.

The mentioned two ingredients in this suitable formula'have'in' common (1) solidification upon evaporation of the water and (2) solubility in'hot water. There are other substances which share these characteristics and would prove suitable for this process.

When used, the composition would be added to water, preferably hot at the time of addition, and, although more concentrated mixtures and more dilute mixtures perform very well, we have found that adding one part of our product to ten parts of hot water gives a mixture with good all-around performance.

The water temperature we have found satisfactory both from material performance standpoint and heating economy is about 150 F. This temperature assists in the cleaning of the discontinuities, keeps the solution at a low viscosity, and speeds the drying action once the test body is removed from the hot solution. This inven tion is not limited to a 150 F temperature as temperatures as low as F and as high as 205 F give satisfactory performance and the range from 120 to 205 F adds versatility to the process. If faster drying is needed, the higher temperature could be used, if lower fuel expense is the objective, a lower temperature would be selected. The F temperature is cited as a practical temperature for this invention.

Once the solution is substantially dry, and in a nonliquid state, the composition on the surface is removed. Using a water-soluble dye in very minute quantities, it is possible to make a reasonably accurate judgement as to when the surface is dry. While water is present, the surface will be the color of the water-soluble dye, but as the water dries the color fades to where it is either not apparent at all or is far less apparent. For example, a small amount of Rhodamine B Extra Base, a product of GAF Corporation, New York, New York, added to the composition mentioned in a preceeding paragraph gives the solution a red or pink color under white light but as the water evaporates the pink becomes less noticeable.

When it is determined either by timing, color change, appearance or other means that the solution has dried, the wax-like coating on the surface may be wiped-off mechanically or washed-off with water. The use of ambient temperature water is preferable to hot water for the removal of the surface coating, as this composition is more readily soluble in hot water and with hot water the chance of solubilizing flaw-retained composition increases. The use of hot water wash would require far greater control and would have a tendency to negate the advantage of a solidified flaw-retained composition.

The action of the water-wash should be primarily a scrubbing function or an eroding function on the surface coating. The flaw-retained wax-like composition, protected by the walls of the flaw, will have far less exposure to the scrubbing or erosion effect of the water as it flows over the surface plane. Slow to dissolve in water at normal tap water temperatures, resistant to dislodgment due to its solid state, the flaw-retained wax-like composition of this formula is less susceptible to over-removal than similar compositions that do not dry to a solid or wax-like state.

Until our discovery, only materials which remained in liquid form were considered suitable for surface flaw detection purposes. For example, reference is made in U.S. Pat. No. 3,349,041, cited as a reference herein, that the composition would include ingredients such as normally liquid water-soluble ethoxylated alkylphenol, normally liquid water-insoluble ethoxylated alkylphenol and normally liquid glycol.

We claim:

1. A method of detecting the presentce of claws in the surface of metallic, ceramic, and glass articles, the steps comprising applying to the surface of said article a coating of a water solution containing a normally solid chemical composition dissolved therein and coloring material, said solution having a temperature of between 120 F and 205 F., allowing said coating to dry on said surface until said coating is solid, removing from the surface said solid coating which has not penetrated said flaws by washing with water, drying said surface, and examining said surface for colored marks.

2. The method described in claim 1 but with the additional step of applying a developing agent.

3. The method described in claim 1 in which the coloring material is one or more fluorescent dyestuffs and the surface is examined under ultra-violet light.

4. The method described in claim 1 in which the normally solid chemical composition includes an ethoxylated nonionic surfactant which is normally solid with a melting point higher than F.

5. The methd described in claim 2 in which the coloring material is one or more fluorescent dyestuffs and the surface is examined under ultra-violet light.

6. The method described in claim 2 in which the normally solid chaemical composition includes an ethoxylated nonionic surfactant which is normally solid with a melting point higher than 90F.

UNITED STATES PATENT OFFICE CERTIFICATE CORRECTION Patent No. 3,777, 19 Dated m r E, 1973 Inventor(s) Dale D winans, 61 al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line :62, liquid should read liquids Column '5, line 9, "presentce" should read N presence line "claws" should read flaws line 29, "methd" should read method line 33, chaemrnloal should read chemical Signed and sealed this 30th. day of April 197A.

' (SEAL) Attest:

EDWARD I LFLETCl-LERJR. C. MARSHAL-L DAMN Atte sting Officer Commissioner of Patents FOB". PQ-wo (10-69) I 'uscoMM-oc coon-Pee a q.s aovznmzqqr rm 'ri'rms dines: nu 0-366-334. 

2. The method described in claim 1 but with the additional step of applying a developing agent.
 3. The method described in claim 1 in which the coloring material is one or more fluorescent dyestuffs and the surface is examined under ultra-violet light.
 4. The method described in claim 1 in which the normally solid chemical composition includes an ethoxylated nonionic surfactant which is normally solid with a melting point higher than 90* F.
 5. The methd described in claim 2 in which the coloring material is one or more fluorescent dyestuffs and the surface is examined under ultra-violet light.
 6. The method described in claim 2 in which the normally solid chaemical composition includes an ethoxylated nonionic surfactant which is normally solid with a melting point higher than 90*F. 